Ajax调用中的解析器错误

Question

I am trying to call controller method from html page through Ajax call and the script is as below,

<script>
    $.ajax({
        url: '/Controllet/getAuth',
        type: "Post",
        data: {
            token: "skgdajshdgfyvbjgydsa",
            userId: "user1"
              },
            cache: false,
            dataType: "json",
            async: true,
            contentType: false,
            processData: false,
            success: function (response) {
                if (response != null && response.success) {
                    alert(response.responseText);        
                } else {
                    //do something else
                }
            },
            error: function (xhr, status, err) {
                alert('Response code:' + xhr.status);
                alert('[Error:' + err + '] ' + status);
            }
        });

My controller method looks like this

private async Task<JsonResult> GetAuth(string token, string userId)
{
    try
    {
        //do something
        return Json(new { success = true, responseText = "!" },
        JsonRequestBehavior.AllowGet);
    }
    catch (Exception ex)
    {
        return Json(new { success = false, responseText = " "
        + ex.Message }, JsonRequestBehavior.AllowGet);
    }
}

Every time I run this I get the [Error:SyntaxError: Unexpected token < in JSON at position 2] parsererror